The invention relates to a cable broadcasting system in which operation modes of a tap device, an amplifier and the like provided on a transmission line for transmitting broadcasting signals are set by command signals transmitted from the center equipment to a transmission
Heretofore, in a cable broadcasting system such as a CATV system where broadcasting signals such as television signals and the like are transmitted to a subscriber""s terminal via a transmission line, various electronic devices for transmitting broadcasting signals such as an amplifier for amplifying broadcasting signals, a tap device for branching the broadcasting signals (the so-called tap-off) from the transmission line and transmitting the signals to the subscriber""s terminal are equipped on the transmission line.
Some of such electronic devices for the cable broadcasting system are known to be provided with receiving circuits and control circuits for setting operation modes so that the operation modes can be automatically set by command signals transmitted to the transmission line from the center equipment.
For example, a relay that can transmit broadcasting signals of high frequency with a small loss is provided in the signal pass between a directional coupler by which broadcasting signals are partially branched from a transmission line and a tap output terminal outputting the branched broadcasting signals to the subscriber""s terminal. The relay is the so-called high frequency relay. Usually, a latching relay capable of keeping the condition of on or off is used. In the above-mentioned electronic device, or the tap device, it is designed that by supplying the relay with electricity in response to a command signal transmitted from the center equipment via the transmission line, the condition of on or off of the signal pass is easily changed (that is, the broadcasting signal is transmitted to the subscriber""s terminal or not) from the center equipment.
In a cable broadcasting system equipped with such electronic devices, a characteristic identifying data (simply referred to as an address, hereinafter) is given to an electronic device capable of setting operation modes. When the center equipment sets the mode of a specific electronic device, the center equipment produces a command signal by adding a command data (also called only xe2x80x9ccommandxe2x80x9d, hereinafter) indicating a content of the command to the address of the corresponding electronic device and transmits the command signal to the transmission line after converting it to a command signal for transmission.
As a result, in the electronic device like the tap device provided on the transmission line, command signals transmitted from the center equipment are received by the receiving circuit, a command signal having the same address as its own address is selected among the received command signals by a control circuit and the operation mode is set according to the command contained in the command signal.
Therefore, in such a kind of cable broadcasting system, the operation mode of the electronic device can be easily set by the center equipment such that, for example, a command signal to a specific tap equipment is transmitted from the center equipment to stop broadcasting signals to the subscriber""s terminal from the tap output terminal of the tap device. In the case, there is no need for the operator to visit the place where the electronic devices are equipped for setting the operation mode of the electronic devices.
However, in such a conventional cable broadcasting system, normal command signals can not occasionally be transmitted because of noises occurring at the periphery of the transmission line, despite that command signals are transmitted to the electronic devices on the transmission line from the center equipment
Specifically, by noises superimposed at the periphery of the transmission line, several bits of the data constituting the command signal are possibly dropped off or some bit data are reversed from xe2x80x9c1xe2x80x9d to xe2x80x9c0xe2x80x9d or vice versa. In such a case, normal command signals can not be transmitted and therefore the operation mode can not be set as desired.
On the other hand, in the field of communication for transmitting data, it is known that the same data are transmitted repeatedly and continuously to overcome the noises. Therefore, also in the cable broadcasting system, such a method is thought to be applied for transmitting command signals from the center equipment to the electronic devices on the transmission line and is being put to practical use. Specifically, in order to transmit surely the command from the center equipment to the targeted electronic devices, the same signals are transmitted repeatedly and continuously from the center equipment and the operation mode is set according to one of the received normal command signals among the continuous command signals in the electronic device.
However, according to such a method, though it is effective when noises are sporadically superimposed at the periphery of the transmission line, it could be a problem that the electronic devices confronted with an instantaneous power failure as well as electronic devices positioned at the terminal side than the electronic devices can not receive any of the command signals, when, for example, by a thunderbolt, the instantaneous power failure that instantaneously shuts power supply to the electronic devices on the transmission line occurs.
Specifically, since the duration time of the instantaneous power failure is 0.2 second at the longest, it does not heavily influences the transmission of broadcasting signals but the duration time of the instantaneous power failure is extremely long compared with the time of the sporadic noises superimposed at the periphery of the transmission line. Therefore, according to the above-mentioned conventional method against noises, the period of time when the same data are transmitted repeatedly and continuously and that of the instantaneous power failure could overlap each other and, as a consequence, occasionally the data can not be transmitted to the electronic devices on the transmission line.
An object of the invention is to provide a cable broadcasting system in which operation modes of various electronic devices such as tap devices, amp lifiers and the like provided on a transmission line are set by command signals transmitted from a center equipment to the transmission line, wherein the command signals can be surely transmitted to the electronic devices even when an instantaneous power failure occurs in the system due to a thunderbolt and the like.
In a cable broadcasting system of the invention, the center equipment is provided with a broadcasting equipment and a transmission equipment. In addition to broadcasting signals outputted from the broadcasting equipment, command signals outputted from the transmission equipment are transmitted to a transmission line. The command signal is a signal for setting operation mode of an electronic device (for example, above-mentioned tap device, amplifier and the like) provided on the transmission line. The electronic device capable of setting operation mode of itself automatically by receiving the command signal as well as a power supply device for supplying the electronic device with electricity are provided on the transmission line.
In the electronic device on the transmission line, a receiving circuit receives the command signal transmitted from the center equipment via the transmission line, a control circuit sets its own operation mode in response to the command signal when the command signal is a command signal to itself, a power source circuit takes in a power signal supplied to the transmission line by the power supply device and converts the power signal to a voltage for operation to supply the built-in circuits like the receiving circuit and control circuit with electricity
In such a cable broadcasting system, it is difficult to transmit a command signal to an electronic device on a transmission line without fail, if the command signal is transmitted only once. Even if command signals are transmitted several times continuously as a conventional system, the command signals can not be transmitted to the electronic device when the transmission period overlaps a period of power failure.
In the invention, when an electronic device whose operation mode is to be set is designated in the transmission equipment of the center equipment from the outside, a transmission data producing means produces a transmission data including an identification data for identifying the electronic device and a command data indicating command content. Then, a transmission data outputting means gives the transmission data a number data indicating a number of transmission and outputs the transmission data given with the number data several times at intervals of a predetermined time longer than the duration time of power failure occurring in the system. Subsequently, the transmission means converts the transmission data to a command signal for transmission and transmits it to the transmission line.
As a result, even when a command signal firstly transmitted from the center equipment could not be sent correctly to the targeted electronic device due to instantaneous power failure induced by a thunderbolt, command signals transmitted from the center equipment later at intervals of a predetermined time can be sent to the electronic device. Therefore, according to the invention, the probability of setting operation mode for electronic devices on the transmission line in response to command signals from the center equipment becomes higher and the reliability is enhanced compared with a conventional cable broadcasting system.
In order to enhance the reliability of the system by raising the probability, the number of command signal transmission carried out at intervals of a predetermined time may be increased. Duration time of instantaneous power failure occurring in the cable broadcasting system is 0.2 second at the longest, so 0.2-0.5 second is preferable to be set as the interval of command signal transmission.
In the transmission equipment of the center equipment, the transmission data outputting means gives the transmission data produced by the transmission data producing means the number data indicating transmission number when transmitting the transmission data to the transmission means for preventing the operation mode from being set plural times in the electronic device by receiving the same command signals transmitted in response to one transmission command in the center equipment, by confirming the transmission number of the received command signal by the number data in the electronic device, and to make it possible to set operation mode corresponding to a command signal transmitted in response to a different transmission command from the center equipment, even if content of the command signal is the same.
Since the transmission data outputting means outputs the transmission data plural times to the transmission means at intervals of a predetermined time, when a new transmission data produced by the transmission data producing means after a transmission data to a specific electronic device is produced by the transmission data producing means and outputted once, the new transmission data is outputted to the transmission means. Therefore, the same command signals are not always transmitted continuously from the transmission means to the transmission line.
Consequently, in case of a conventional system in which an electronic device simply determines whether the same command signals are continuing and sets the operation mode in response to one of the command signals if the same signals are confirmed to be continuing, the electronic device sets the operation mode as if the command signals are all different and so the operation mode is unnecessarily set, when a different command signal is inserted between the same command signals.
In order to solve the problem, a method is proposed that when the electronic device on the transmission line determines that the content of a command signal from the center equipment is the same to that of a command signal used for the previous setting of operation mode, the electronic device stops setting of operation mode responding to the command signal.
However, the command signal from the center equipment is transmitted to the transmission line in response to a command from the outside. Command signals with the same content are occasionally transmitted continuously plural times to the same electronic device in order to make the electronic device carry out compulsorily the same setting operation plural times.
In such a case, command signals with the same content are transmitted at intervals of a predetermined time and at the same time, another command signal with the same content is added further between transmission of the command signals. As a result, when execution of unnecessary setting operation is stopped by simply determining whether content of the command signal is the same or not, setting of the same operation mode can not be carried out plural times in response to demand of the center equipment.
Such demand for executing the same operation mode setting plural times occurs, for instance, when operation mode of an electronic device is tried to be restored by making the electronic device carry out operation mode setting plural times, in response to complaint from the subscriber that he can not receive broadcasting signals.
In the invention, command signals are not only transmitted from the center equipment at intervals plural times but also number data indicating transmission number are transmitted at the same time. The electronic device which receives the command signals can determine whether the command signal from the center equipment is a command signal the electronic device has already used for the operation mode setting, based on the number data.
For the purpose, in the control circuit in the electronic device of the invention, the command signal identifying means determines whether a command signal received by the receiving circuit is a signal to the electronic device or not, based on identification data constituting the command signal. When the command signal is determined to be for the electronic device, the command content determining means determines whether the command data constituting the command signal is the same as a previously received command signal for the electronic device. When the command data is the same as the previously received command data, the transmission number determining means determines whether a number data given to the new received command signal is larger than the number data given to previously received command signal for the electronic device.
Then, when the number data is determined to be larger than the previously received number data by the transmission number determining means, operation mode setting based on the new received command signal is not carried out by the operation mode setting means for actually setting operation mode. When the number data is determined to be equal to or smaller than the previously received number data by the transmission number determining means or the command data of the new received command signal is different from that of the previously received command signal by the command content determining means, setting of operation mode of the electronic device is carried out in response to the new received command signal.
Therefore, according to the invention, command signals can not only be surely transmitted to the electronic device from the center equipment without being influenced by noises occurring in the periphery of the system, the electronic device can set operation mode using one of command signals transmitted from the center equipment in response to commands from the outside, thereby unnecessary setting operation based on duplicated command signals being surely prevented from occurring.
Since operation mode setting by the electronic device can be suppressed to the minimum, electricity consumption for unnecessary operation mode setting can be reduced, even if the electronic device is a device (for example, the above-mentioned tap device for changing over output or stop of broadcasting signals from output terminals by supplying relays with electricity) whose electricity consumption is increased by operation mode setting, thereby load on the power supply device provided on the transmission line being decreased.
According to the invention, the center equipment is constituted such that command signals based on commands from the outside are transmitted plural times at intervals of a predetermined time. Number of transmission data per one command signal transmission carried out by the center equipment may be one or more.
When the number of transmission data per one transmission is plural, even if one of the transmission data can not be transmitted to the electronic device on the transmission line due to sporadic noises in the periphery of the system, the operation mode of the electronic device can be set by anther continuing transmission data. Therefore, the probability of transmission of normal transmission data to the electronic device becomes high and operation mode of the electronic device can be set more quickly.
According to a cable broadcasting system of another aspect of the invention, as mentioned above, number of transmission data sent from the center equipment to the transmission line per one transmission at intervals of a predetermined time is plural to transmit command signals (data) to the electronic device on the transmission line more quickly and more surely.
Specifically, in the cable broadcasting system of the invention, when the transmission data outputting means transmits transmission data at intervals of a predetermined time, plural transmission data made by adding the same number to the transmission data are continuously outputted. When command signals consisting of the same transmission data are received by the receiving circuit continuously, the control circuit of the electronic device selects one of the signals as a command signal transmitted by the center equipment and operates each means for setting operation mode (the command signal identifying means, command content determining means, transmission number determining means and operation mode setting means) by using the selected command signal.
Therefore, in the cable broadcasting system of another aspect of the invention, plural command signals consisting of the same transmission data produced in the transmission data producing means are transmitted continuously and groups of the continuing command signals are transmitted plural times at intervals of a predetermined time. The electronic device takes in one of the same continuing command signals as a command signal from the center equipment.
Therefore, according to another aspect of the invention, even when command signals are influenced by sporadic noises that occur in the periphery of the system during transmission of command signals from the center equipment, the electronic device on the transmission line sets operation mode in response to the same command signal transmitted continuously next to the command signal from the center equipment. As a result, the probability of transmission of normal transmission signals is heightened and operation mode of the electronic device can be set more quickly.
In a cable broadcasting system of a further aspect of the invention, the above-mentioned tap device is provided as an electronic device for setting operation mode by receiving command signals from the center equipment in either of the previously described broadcasting systems.
Specifically, the tap device is provided with a directional coupler which branches a part of broadcasting signals and outputs the branched broadcasting signals from a tap output terminal to a terminal device. In a signal pass from the directional coupler to the tap output terminal, a latching relay for changing over the condition of on or off of the signal pass is provided. The control circuit sets the condition of on or off of the signal pass by the latching relay by controlling the operation circuit in response to a command signal from the receiving circuit. The operation circuit changes over the condition of on or off of the signal pass by turning on the latching relay under the control of the control circuit. The power source circuit takes in power signal from the power supply device via the transmission line and supply the receiving circuit, control circuit and operation circuit with electricity.
Therefore, according to the cable broadcasting system of the further aspect of the invention, each tap device on the transmission line sets output or stop of broadcasting signals from the tap output terminal using one of plural command signals transmitted from the center equipment responding to one command and does not carry out unnecessary setting operation corresponding to another one of the same command signals. Hence, according to the further aspect of the invention, number of turning on or off of the latching relay carried out for setting output or stop of broadcasting signals by the operation circuit in the tap device can be suppressed to the minimum, thereby electric consumption of the tap device used for turning on the latching relay being also suppressed to the minimum. According to the further aspect of the invention, output or stop of broadcasting signals from the tap output terminal of the tap device can not only be set surely by transmitting command signals from the center equipment to the tap device without fail, but also the load on the power supply device on the transmission line is alleviated by decreasing electricity consumption used for the setting and the power supply device can be made small by lowering its capacity.
In a cable broadcasting system of the furthest aspect of the invention, the tap device on the transmission line in the above-mentioned broadcasting system is provided with a splitter for further branching broadcasting signals branched by the directional coupler and outputting the further branched broadcasting signals to the plural tap output terminals. The tap device is provided with a latching relay on each of plural signal passes from the splitter to the tap output terminals. When the control circuit controls the condition of on or off of each signal pass in response to command signals received by the receiving circuit, the control circuit turns on each latching relay to set the condition of on or off of each signal pass in order by operating the operation circuit.
In the system, the latching relays for setting output or stop of broadcasting signals are supplied with electricity not at the same time but one by one in order.
Therefore, according to the furthest aspect of the invention, not only the same effect as the above-mentioned broadcasting system can be attained, but also electricity instantaneously consumed when setting output or stop of broadcasting signals from the plural tap output terminals in the tap device can be suppressed to the minimum.
Specifically, when setting output or stop of broadcasting signals from plural tap output terminal, plural latching relays in the signal passes may be turned on the electricity at the same time. But by doing such operation, quantity of electricity supplied to the tap device from the transmission line temporarily becomes extremely large and capacity of the power supply device has to be large enough to supply such large quantity of electricity.
However, according to the furthest aspect of the invention, when output or stop of broadcasting signals from plural tap output terminals is to be set, quantity of electricity flowing into the tap device can be restricted to the same quantity as that for a tap device with one tap output terminal (specifically, quantity of electricity necessary for operating one latching relay) and so capacity of the power supply device can be made small.